Broiler chick starter diets contain a considerable amount of crude protein. Most of the crude protein is obtained from traditional feed ingredients such as soybean meal. Approximately 90% of the crude protein present in soybean meal (48% crude protein content) is highly digestible for poultry (National Research Council (1994). Nutrient requirements of poultry. 9th revised Ed. National Academy Press, Washington, D.C.). Although the traditional corn-soybean meal broiler starter diets are considered highly digestible, they often contain a variety of complex proteins that are not easily digested by a young chick due to the lack of necessary innate enzymes at early stages of life (Uni, et al. (1999) Poultry Sci. 78: 215-222). Inclusion of proteases in broiler diets has been suggested, but much of the early work with protease addition to cereal grain-based diets did not result in any improvements in bird performance (Jensen, et al. (1957) Poultry Sci. 36: 919-921).
More recently, enzyme supplementation of poultry diets with enzyme mixtures, including proteases and amylases, has produced some improvements in growth performance (Greenwood, et al. (2002) Poultry Sci. 81 (Suppl. 1): 25; Burrows, et al. (2002) Poultry Sci. 81 (Suppl. 1): 29; Short, et al. (2002) Poultry Sci. 81 (Suppl. 1): 136). Supplementing a corn-soybean broiler starter diet with an enzyme preparation containing a mixture of xylanase, protease, and amylase resulted in improvements in body weight at 14 and 42 days of age with no significant effects on feed conversion ratio (Greenwood, et al. (2002) supra). Upon supplementing corn-soy based duck diets with the same enzyme mixture, the enzyme supplementation resulted in improvements in body weight gain and feed conversion ratio (Burrows, et al. (2002) supra).
Poultry feed further contains some complex antinutritional and/or indigestible compounds. Some of these compounds, such as the nonstarch polysaccharides, absorb water into a viscous mass within the chyme from which nutrients are not readily absorbed (Odetallah, 2000; Odetallah, et al. (2002) supra). As chyme viscosity increases, the rate of diffusion of digestive enzymes and nutrients decreases, thus impeding nutrient absorption by the enterocyte. Fat micelle formation and absorption also decrease as chyme viscosity increases, thus impairing absorption of many of the fat-soluble compounds, including fat-soluble vitamins, pigments, and lipids (Ferket and Veldkamp (1999) In: Proceedings of the 1998 World Poultry Science Association, pgs 43-52). Therefore, viscosity reduction achieved by endolytic enzyme activity may play a role in the improvement seen in young chicks fed high-viscosity cereals, and the relative effectiveness of various enzymes appears to be related to their viscosity-reducing capability (Roger, et al. (1990) J. Sci. Food Agric. 50:19-27).
PWD-1 keratinase is an enzyme that was originally purified from the growth medium of Bacillus licheniformis PWD-1 (Williams, et al. (1990) Appl. Environ. Microbiol. 56:1509-1515; Lin, et al. (1992) Appl. Environ. Microbiol. 58:3271-3275). PWD-1 keratinase hydrolyzes a broad range of protein substrates including casein, collagen, elastin and keratin (Shih (2001) In: Proceedings International Conference of Agricultural Science and Technology, Beijing, China, pgs 244-247). PWD-1 keratinase has been used to produce hydrolyzed feather meal by incubating commercial feather meal with cell-free keratinase overnight (Carter (1998) Bacterial Keratinase: Assay development and nutritional application. Ph.D. Thesis, North Carolina State University, Raleigh, N.C.). See also U.S. Pat. Nos. 4,908,220; 5,186,961; and 5,063,161 to Shih et al.
In spite of the foregoing, there remains a need for additional methods of enhancing growth performance of broiler chicks and animal feed supplements that accomplish the same.